The Plant That Ate Dirty Socks Gets a Girlfriend, Paperback/Nancy McArthur

Michael and Norman and their giant weird sock-eating plants, Stanley and Fluffy, meet an amazing girl plant who takes a fancy to Stanley when the family's botanist friend and her daughter and son come to visit. After a hilarious sleepover, a visit to a zoo rainforest exhibit, and Norman's attempts to teach Fluffy karate, the three plants team up to foil some bad guys.